Constant Joining Material in Air Vortex Spinning Methods

ABSTRACT

The present application relates to a method for operating a drafting arrangement ( 1 ) for drafting a fibre composite ( 2 ). For this purpose, the drafting arrangement ( 1 ) has at least one front pair of rollers ( 3 ) and one rear pair of rollers ( 4 ) having a nip line ( 5 ), a fibre composite end ( 6 ) being present for operating the drafting arrangement ( 1 ). According to the invention, when the drafting arrangement ( 1 ) is put into operation, the fibre composite end ( 6 ) enters the nip line ( 5 ) of the rear pair of rollers ( 4 ) only when the build-up arising from acceleration has ended in the rotational speed profile of the front pair of rollers ( 3 ) and in the rotational speed profile of the rear pair of rollers ( 4 ).

The present invention relates to a method for operating a drafting arrangement, according to the precharacterizing clause of the independent Patent Claims 1 and 2, to a control for drafting arrangements of a textile machine, according to the precharacterizing clause of Patent Claim 12, and to a textile machine having a said control, according to Patent Claim 13.

PRIOR ART

Methods for operating drafting arrangements are known in textile technology. The publications EP 121 97 37, EP 807 700 and EP 137 57 09 describe methods of this type. However, as is evident from the publications mentioned, the present invention is suitable particularly for the operation of drafting arrangements which belong to air-spinning machines. In air-spinning machines, a fibre composite is spun into a yarn by means of one of more airflows.

The known methods for operating a drafting arrangement, however, have disadvantages. This applies particularly to drafting arrangements which belong to air-spinning machines or to drafting arrangements which transfer the drafted fibre composite to a spinning unit operating according to an air-spinning method. The disadvantage of the known methods for operating a drafting arrangement is that the piecer quality is not always satisfactory. The term “piecer” is understood to mean a “seam”, within a yarn, at which the yarn has been “pieced up” or “hung up” again, for example after an interruption in production. Normally, a piecer is produced by spinning further fibres at or around an existing yarn end. The piecer constitutes an actual overlap region between a yarn end and new fibres additionally spun on this. It therefore often forms a thick place which is actually undesirable. Ideally, a piecer or a piecing point should not differ from the remaining yarn, this applying particularly to strength and fibre mass. In an endeavour to achieve this ideal state, various possibilities are disclosed in the abovementioned publications. For example, the fibre end at which piecing is to take place may be narrowed and/or the drafting arrangement delivers fewer fibres in the overlap region than in the subsequent stationary operating state. Irrespective of this, however, in the known devices, there is a further problem which the present invention now intends to solve.

To be precise, it was found that, when a drafting arrangement is put into operation and therefore when the associated pairs of rollers are put into operation or accelerated, a build-up of the rotational speed profile to the corresponding piecing speed takes place. This build-up (overshoots and undershoots), which is caused by the run-up of the pairs of rollers from standstill to their corresponding piecing speed or piecing rotational speed (see FIG. 2 and the later description), gives rise, when the piecing rotational speed is first reached, to a non-constant rotational speed profile of the pairs of rollers and therefore to a non-constant rotational speed ratio between the pairs of rollers of a drafting arrangement. Normally, in a drafting arrangement, the piecing operation commences during the acceleration of the pairs of rollers to an operating speed or immediately after a fixed piecing speed is reached. In other words, the build-up of the pairs of rollers during their acceleration to the piecing speed has never been taken into account hitherto in the production of a piecer. This has hitherto given rise to a piecer obtained at non-constant rotational speeds or a non-constant rotational speed ratio between the two pairs of rollers of a drafting arrangement which cause the draft. To be precise, due to the overshooting and undershooting of the pairs of rollers, an inaccurate or varying draft occurs in the fibre composite. When this varyingly drafted fibre composite is combined with a yarn end, thus giving rise to a piecer, this piecer, too, has mass fluctuations. The result of this is that, in the overlap region of the piecer, an inadmissible thick place mostly occurs, often followed by an inadmissible thin place. Conversely, a thin place occurs in the overlap region or piecing fails completely.

The object on which the invention is based is, therefore, to provide a method for operating a drafting arrangement for the drafting of a fibre composite, by means of which mass fluctuations in the piecer are avoided or minimized. An object which may also be considered is to provide a method for operating a drafting arrangement, in which a fibre composite is to be drafted from the outset with the correct draft ratio.

This or these objects is or are achieved by means of the features in the independent Patent Claims 1 and 2.

The advantageous effect of the method according to the invention is now explained below with reference to FIGS. 1 and 2.

FIG. 1 shows a typical drafting arrangement 1, at which the method according to the invention can be used. For this purpose, the drafting arrangement 1 has a front pair of rollers 3 and a rear pair of rollers 4 having a nip line 5. The drafting arrangement 1 may have a further pair of rollers 7. The drafting arrangement 1 serves for drafting the fibre composite 2. For this purpose, the pairs of rollers 3 and 4 rotate at different speeds or circumferential speeds. The front pair of rollers 3 and the rear pair of rollers 4 consequently form what is known as the main drafting zone 8 of the drafting arrangement 1. Drafting may also take place between the pairs of rollers 7 and 3 (what is known as predraft). As a rule, a drafting arrangement, such as is illustrated in FIG. 1, has at the front pair of rollers 3 aprons 20 which serve for guiding the fibre composite 2 to be drafted. However, the presence of the aprons 20 is not essential to the invention or is not absolutely necessary. During stationary operation, the fibre composite 2 runs through the pair of rollers 7 (if present) and, above all, through the pairs of rollers 3 and 4. In this case, the fibre composite 2 is drafted and leaves the drafting arrangement 1 at or downstream of the nip line 5 of the rear pair of rollers 4. The drafted fibre composite is thereafter mostly further-processed in the same way (for example, at a spinning unit, see, in this respect, the following FIG. 4). If, then, for any reason, an interruption in production takes place or the drafting arrangement 1 generally has to be put into operation again, the fibre composite 2 has to be introduced into the drafting arrangement 1 again or at least correctly positioned. The position of the fibre composite end 6 therefore assumes a particularly important role. It is unimportant for the invention whether the drafting arrangement 1 in this case has the additional pair of rollers 7 or even also a further pair of rollers. It is normally such that, in the event of an interruption in production, the pairs of rollers of the drafting arrangement 1 are stopped in a sequence whereby the fibre composite 2 is broken away at the nip line 5. For this purpose, the front pair of rollers 3 is stopped before the rear pair of rollers 4. As a result, the fibre composite end 6 is located directly in front of the nip line 5. See, in this respect, for example, the abovementioned EP 137 57 09.

When the drafting arrangement 1 is then put into operation again, first, as a rule, the rear pair of rollers 4 commences to rotate before the front pair of rollers 3 itself resumes operation. It may well be that the period of time between the operation of the rear pair of rollers 4 and that of the front pair of rollers 3 is sufficient to ensure that, in the rotational speed profile of the pair of rollers 4, the build-up arising from acceleration is terminated before the front pair of rollers 3 is set in motion. However, since the fibre composite end 6 is located directly in front of the nip line 5 of the rear pair of rollers 4, a drafting of the fibre composite 2 takes place immediately after the front pair of rollers 3 has been put into operation. Since, after being put into operation, the front pair of rollers 3 still has to accelerate to the piecing speed or operating speed, a build-up to the desired piecing rotational speed also takes place here. As a result, that region of the fibre composite 2 which directly follows the fibre composite end 6 is drafted in a fluctuating manner and consequently has undesirable mass fluctuations. If this “initial region” of the fibre composite 2 is used to produce a piecer, then, of course, this piecer, too, has undesirable mass fluctuations.

That these mass fluctuations occur can also be seen very clearly from FIG. 2. The figure shows, inter alia, the rotational speed profile U₄(t) of the rear pair of rollers 4 and the rotational speed profile U₃(t) of the front pair of rollers 3. At a time point t=0, the rear pair of rollers 4 is put into operation. For this purpose, the said pair of rollers 4 is accelerated for a period of time t_(h,4) until the pair of rollers 4 has reached the piecing rotational speed U_(A,4) (for example, ˜5 mm/msec). The acceleration of the rollers is very high since the yarn end 10 selected must otherwise be unacceptably long. The run-up therefore takes place during a few milliseconds. Since it is not possible, for physical reasons, for the pairs of rollers to break off acceleration abruptly in the case of the constant, but very high accelerations when the desired rotational speed is reached, a build-up occurs during a specific period of time t_(EV,4). The same also applies correspondingly to the front pair of rollers 3 (build-up during the period of time t_(EV,3)). How long this build-up lasts and how great the overshoots or undershoots are depends on the physical properties of the driven pairs of rollers and on their drive, closed-loop control and open-loop control. By suitable closed-loop controls and drives being used, the period of time t_(EV) can be reduced to a minimum. However, because of the high accelerations of the pairs of rollers, it cannot be prevented completely.

So that no mass fluctuations occur as a result of the said effects in the initial region of the drafted fibre composite when a drafting arrangement is put into operation, according to the invention the fibre composite end (that is to say, the foremost tip of the fibre composite) is supplied to the nip line of the second pair of rollers only when both pairs of rollers have ended their corresponding build-ups arising from acceleration. This time point is designated by t_(EVE) in FIG. 2: at this time point, both pairs of rollers have reached a constant piecing rotational speed (as illustrated in the figure) or they have at least ended the build-up. According to the invention, then, the drafting of the fibre composite is recommenced at the earliest at the time point t_(EVE) or, in other words, the fibre composite end should enter the nip line of the rear second pair of rollers and consequently be drafted at the earliest at the time point t_(EVE). If the operation of the drafting arrangement also involves an action of piecing up to a yarn end in addition to this coordinated draft, then the time point for the commencement of the piecing action t_(K) should not lie before the time point t_(EVE). The time point t_(EVE) is therefore the earliest time point for commencing the piecing action. When a piecing action is carried out, this lasts for a few milliseconds (see the period of time t_(AE), for example ˜8 msec) and is concluded at a time point t_(E). With the conclusion of the piecing action at the time point t_(E), the drafting arrangement can be operated in a stationary mode again. The piecing action preferably takes place at a constant piecing rotational speed U_(A,4) or U_(A,3) and, after piecing has taken place, both pairs of rollers can run up synchronously and more slowly, that is to say without overshoots, to their respective operating rotational speed U_(B,3) and U_(B,4). It is perfectly conceivable, however, that piecing takes place virtually at the operating rotational speed, so that the piecing rotational speeds U_(A,3) and U_(A,4) already represent the operating speeds for the stationary operation of the drafting arrangement. The synchronous run-up of the rollers to an operating rotational speed different from the piecing rotational speed is illustrated by dashes in FIG. 2.

There are various advantageous refinements and embodiments of the method according to the invention which are to be found in the dependent claims.

The invention and the idea of the invention or its implementation are explained below with reference to further figures. It is to be pointed out expressly, however, that the invention or the idea of the invention is not restricted to the embodiments shown in the figures and examples.

FIG. 3 shows a drafting arrangement at which a piecing action is to be carried out, the method according to the invention being used in this case for putting it into operation. To carry out the piecing action, first, an existing yarn end 10 is drawn, opposite to the actual spinning direction, through the spinning unit 12 which is arranged downstream of the drafting arrangement. The yarn end 10 is likewise guided through the nip line 5 of the rear pair of rollers 4 and, cut to a specific length, is positioned appropriately for operation. When the drafting arrangement is put into operation, first, the rear pair of rollers 4 commences to rotate, as illustrated in FIG. 2. Only thereafter is the front pair of rollers 3 put into operation. Possibly, even both pairs of rollers are put into operation simultaneously (this corresponds to a possible variant of the method according to the invention). Before the drafting arrangement is put into operation, however, the fibre composite end 6 is brought, as illustrated, to a specific distance from the nip line 5 of the rear pair of rollers 4. This distance is at least such that, when the fibre composite end 6 reaches the nip line 5, both pairs of rollers 3 and 4 have, in the rotational speed profile, ended the build-up arising from acceleration. When piecing takes place, as described further above, parts of the yarn end 10 and of the front region of the fibre composite 2 illustrated overlap one another. This overlap region is spun in the following spinning unit 12 to form the actual piecer.

FIG. 4 shows a drafting arrangement which has been put into operation by means of the method according to the invention, and its following spinning unit 12. The figure shows the drafting arrangement 1 and the spinning unit 12 in a stationary operating state. The individual elements correspond to the preceding figures and are given correspondingly identical reference symbols. The rollers 16 of the rear pair of rollers 4 deliver the drafted fibre composite 11 to the spinning unit 12. The spinning unit 12 can spin the drafted fibre composite 11 according to various spinning methods. This figure illustrates a spinning unit 12 which operates according to an air-spinning method (a vortex-type air-spinning method, as it is known). For this purpose, the spinning unit 12 has a vortex chamber 14 and a spindle 15 contained in the latter. The spindle 15 is, to be precise, a preferably non-rotating spinneret. An air-vortex flow is generated in the vortex chamber 14 by means of nozzles and causes a spinning of the fibres of the drafted fibre composite 11 at the mouth of the spindle 15. The yarn 13 thereby produced is taken up correspondingly and wound (not shown) onto a winding device. As may be gathered from the figure, the drafting arrangement 1 also has the pair of rollers 7 which forms with the pair of rollers 3 a predrafting zone 9. It should also again be pointed out explicitly that the method according to the invention for operating a drafting arrangement is not restricted to a specific spinning method, such as the air-spinning method shown here, or to the presence of the further pair of rollers 7.

FIG. 5 shows a control 19 according to the invention which operates the drafting arrangement 1 by the method according to the invention. For this purpose, the rear pair of rollers 4 has a specific drive 18 and the front pair of rollers 3 likewise has the drive 17. If, as illustrated here, the drafting arrangement 1 also consists of a further pair of rollers 7 which forms with the pair of rollers 3 a predrafting zone, then the pair of rollers 7 can also be driven by the drive 17 of the pair of rollers 3 (or may have an additional specific drive). The control 19 according to the invention controls the drives 17 and 18 correspondingly to the method according to the invention when the drafting arrangement is put into operation. The control 19 may be connected to correspondingly further monitoring and control devices of a textile machine (the textile machine as a whole not being illustrated).

Depending on how the drafting arrangement has previously been stopped, the method according to the invention may also include moving the fibre composite end 6 back from the nip line 5 of the rear pair of rollers 4 before the drafting arrangement is put into operation. This may also take place automatically, for example by means of the control 19 and the drive 17. This applies particularly when the fibre composite end 6 is not separated from the nip line 5 of the rear pair of rollers 4 at a predetermined distance by hand. This is desirable, above all, in fully automatic piecing methods and devices, in which the drafting arrangement is first stopped so that the fibre composite 2 breaks away at the nip line 5 of the rear pair of rollers 4. To be precise, in this case, a clearly defined fibre composite end 6 is obtained, which merely has to be positioned appropriately before the drafting arrangement can be put into operation again.

The invention is not restricted to the possibilities and the embodiments explicitly mentioned. On the contrary, these variants are intended as suggestions for a person skilled in the art in order to implement the idea of the invention as beneficially as possible. Further advantageous uses and combinations which likewise reproduce the idea of the invention and are to be protected by this application can therefore easily be derived from the embodiments described. Some of the disclosed features have been described in combination in this description and are claimed in combination in the following claims. It is also conceivable, however, to claim individual features of this description in themselves or in another combination in application of the idea of the invention. The applicant therefore expressly reserves the right, in any event, to provide other combinations in application of the idea of the invention.

KEY

-   1 Drafting arrangement -   2 Fibre composite -   3 Front pair of rollers -   4 Rear pair of rollers -   5 Nip line -   6 Fibre composite end -   7 Pair of rollers -   8 Main drafting zone -   9 Predrafting zone -   10 Yarn end -   11 Drafted fibre composite -   12 Spinning unit -   13 Yarn -   14 Vortex chamber -   15 Spindle -   16 Rollers of the rear pair of rollers -   17 Drive predraft -   18 Drive rear pair of rollers -   19 Control -   20 Apron -   U₄(t) Rotational speed profile of rear pair of rollers 4 -   U₃(t) Rotational speed profile of front pair of rollers 3 -   U_(A,4) Piecing rotational speed for the rear pair of rollers 4 -   U_(A,3) Piecing rotational speed for the front pair of rollers 3 -   t_(s,3) Time point for operating the front pair of rollers 3 -   t_(h,3) Period of time until the front pair of rollers 3 reaches the     piecing rotational speed U_(A,3) (acceleration) -   t_(h,4) Period of time until the rear pair of rollers 4 reaches the     piecing rotational speed U_(A,4) (acceleration) -   t_(EV,3) Period of time until the front pair of rollers 3 has ended     the build-up arising from acceleration -   t_(EV,4) Period of time until the rear pair of rollers 4 has ended     the build-up arising from acceleration -   t_(K) Time point commencement of piecing action -   t_(E) Time point end of piecing action -   t_(AE) Period of time piecing action -   t_(EVE) Time point in which both pairs of rollers have ended the     build-up -   U_(B,4) Operating rotational speed of the rear pair of rollers 4 -   U_(B,3) Operating rotational speed of the front pair of rollers 3. 

1. Method for operating a drafting arrangement (1) for drafting a fibre composite (2), the drafting arrangement (1) containing a front pair of rollers (3) and a rear pair of rollers (4) having a nip line (5), and a fibre composite end (6) being present for starting up the drafting arrangement (1), characterized in that, before the drafting arrangement (1) is put into operation, the fibre composite end (6) is brought to a predetermined distance from the nip line (5) of the rear pair of rollers (4), this distance preferably amounts to up to 6 mm, this distance preferably amounts to 0.1 mm to 5 mm, this distance particularly preferably amounts to 3 mm or 4 mm, and the bringing to a distance is preferably carried out by the fibre composite end (6) being cut to length. 2-13. (canceled) 